Factors Affecting Winter Survival of Female Mallards in the Lower Mississippi Alluvial Valley

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1 Factors Affecting Winter Survival of Female Mallards in the Lower Mississippi Alluvial Valley BRUCE E. DAVIS 1,*, ALAN D. AFTON 2 AND ROBERT R. COX JR 3 1 School of Renewable Natural Resources, 336 RNR Building, Louisiana State University, Baton Rouge, LA, 70803, USA 2 U.S. Geological Survey, Louisiana Cooperative Fish and Wildlife Research Unit, Louisiana State University, Baton Rouge, LA, 70803, USA 3 RC Store, P. O. Box 712, Ipswich, SD, 57451, USA *Corresponding author; bdavi29@tigers.lsu.edu Abstract. The lower Mississippi Alluvial Valley (hereafter LMAV) provides winter habitat for approximately 40% of the Mississippi Flyway s Mallard (Anas platyrhynhcos) population; information on winter survival rates of female Mallards in the LMAV is restricted to data collected prior to implementation of the North American Waterfowl Management Plan. To estimate recent survival and cause-specific mortality rates in the LMAV, 174 radio-marked female Mallards were tracked for a total of 11,912 exposure days. Survival varied by time periods defined by hunting seasons, and females with lower body condition (size adjusted body mass) at time of capture had reduced probability of survival. Female survival was less and the duration of our tracking period was greater than those in previous studies of similarly marked females in the LMAV; the product-limit survival estimate (±SE) through the entire tracking period (136 days) was 0.54 ± Cause-specific mortality rates were 0.18 ± 0.04 and 0.34 ± 0.12 for hunting and other sources of mortality, respectively; the estimated mortality rate from other sources (including those from avian, mammalian, or unknown sources) was higher than mortality from non-hunting sources reported in previous studies of Mallards in the LMAV. Models that incorporate winter survival estimates as a factor in Mallard population growth rates should be adjusted for these reduced winter survival estimates. Received 7 May 2010, accepted 24 October Key words. Anas platyrhynchos, Arkansas, Louisiana, Mallard, Mississippi Alluvial Valley, seasonal survival, radiotelemetry, winter. Waterbirds 34(2): , 2011 The Mallard (Anas platyrhynhcos) is a temperate nesting dabbling duck (Anas spp.) that commonly winters in the southern half of the United States. The lower Mississippi Alluvial Valley (hereafter LMAV) contains the continent s greatest concentration of wintering Mallards (Bellrose 1976). Given the large number of Mallards wintering in this region, seasonal survival could have important effects on midcontinent Mallard populations. Studies using radio-telemetry have reported high winter survival rates for Mallards in the LMAV. Mean survival rates of 0.82 were reported for a 70-day monitoring period for radio-marked female Mallards during the 1980s in the LMAV, and no deaths were observed among female Mallards marked between the end of hunting seasons and February in another study during 1988 and 1989 (Reinecke et al. 1987; Dugger et al. 1994). Recent studies have reported lower survival rates for wintering Mallards in coastal Louisiana and in Colorado (Link 2007; Dooley 2008), but recent survival estimates were not available for the LMAV. Previous radio-telemetry and reward band studies indicated that hunting was the primary mortality agent for Mallards within the LMAV (Blohm et al. 1987; Reinecke et al. 1987). Conversely, for Mallards in the Playa Lakes region of Texas, non-hunting mortality was greater than hunting mortality (Bergan and Smith 1993). Previous studies indicate that half of the female Mallards wintering in the LMAV remained until mid-march (Dugger 1997); data on survival of Mallards remaining in the LMAV during February, March and early April may improve our understanding of overall survival during the non-breeding season. Various studies have examined the influence of female age, body condition, winter of study and time periods within winters on 186

2 MALLARD SURVIVAL IN WINTER 187 survival of Mallards. Data from radio-telemetry and banding studies have indicated that adults survived at higher rates than did immatures (Reinecke et al. 1987; Blohm et al. 1987). In some studies, survival has been positively correlated with early season body condition during winter (Bergan and Smith 1993; Jeske et al. 1994). Annual variation in regional water levels did not affect survival in previous radio-telemetry studies of Mallards; however, annual variation in water levels may not have been great enough to influence survival in these studies. Our study included one extremely wet and one extremely dry winter; thus, detection of a relationship of winter to survival could indicate a response to differing regional water conditions between winters. Hunting and disturbance may alter movement patterns and habitat use by Mallards (Stafford et al. 2007). Detection of changes in survival rates among time periods defined by hunting seasons (hereafter, seasons) may reveal responses to disturbances caused by hunting and related activities. Recent data on survival and cause-specific mortality rates and the factors influencing these rates could provide important information about Mallard populations in the LMAV. Strategies that reduce vulnerability to mortality agents could be implemented if increasing non-breeding season female Mallard survival becomes a management objective in the LMAV. Incorporation of recent winter survival estimates as a factor in Mallard population growth models should result in increased accuracy of those models. Our objectives were to estimate recent survival rates and identify cause-specific mortality factors for female Mallards in the LMAV. We examined variation in survival in relation to the following covariates and their potential two-way interactions: female age, body condition at time of capture, winter of study and seasons. Study Site Our trap sites were located on the Mollicy Unit of Upper Ouachita National Wildlife Refuge (NWR), 19.5 kilometers (km) east and 5 km north of Marion, Louisiana. Our core radio tracking area included all lands within 80 km of our trap sites and encompassed a portion of the LMAV in northeastern Louisiana and southeastern Arkansas (Fig. 1). These areas contained a complex mosaic of habitats including forested wetlands, areas being actively reforested, managed moist soil areas, agricultural areas farmed for rice, rice agricultural areas left idle, areas planted in other crops and areas used for grazing livestock (Davis et al. 2009). The western third of the core tracking area was dominated by pine silvaculture and received little use by marked females (Davis 2007). Our extended search area included all of the LMAV (described in detail by Delnicki and Reinecke 1986) and a portion of southwest Louisiana. We searched the extended tracking area to differentiate between females emigrating from the core tracking area and those with failed transmitters. Field Methodology We captured and radio-marked 91 (61 adult and 30 immature) and 98 (51 adult, 46 immature, and one unknown age) female Mallards from 27 November through 15 December 2004 and from 19 November through 22 November 2005, respectively (see Davis et al. 2009). Females were captured using swim-in traps adapted from those described by Mauser and Mensik (1992) or with rocket nets fired from portable platforms (Dill and Thornberry 1950; Cox and Afton 1994). We baited traps and rocket nets with varying mixtures of METHODS Figure 1. Core tracking area (solid circle), extended search area (dashed polygon), and trapping areas at Upper Ouachita NWR (polygon in center of circle) for radio-marked female Mallards during winters and in the lower Mississippi Alluvial Valley.

3 188 WATERBIRDS rice, wheat, corn and sweet potatoes and attempted to capture birds as soon as possible after their arrival in our study area. We banded captured females and aged them as immature (hatched during yr of capture) or adult (hatched prior to yr of capture) according to wing plumage characteristics (Carney and Geis 1960). We marked females using 21-g harness-type transmitters (Dwyer 1972; Advanced Telemetry Systems; Isanti, MN) and a standard aluminum leg band and recorded mass (±10 g), flattened and natural wing chord (±1 mm), and total tarsus, head length, culmen and middle toe (±0.05 mm; Dzubin and Cooch 1992). Immediately prior to weighing and marking, we palpated each female s neck to determine the presence and amount of bait, which was easily detected, and scored its esophageal contents as full, medium or empty. We provided food and water ad libitum for all captured ducks held for instrumentation and measurements and released them at capture sites 24 hours after capture. We captured and handled ducks in accordance with Louisiana State University s Institutional Animal Care and Use Committee protocol # and marked them under authority of USGS banding permit number Transmitters had an expected battery life of 160 days and were equipped with mercury-type mortality switches that doubled pulse rates if transmitters remained motionless for 4 hours; use of these switches decreased recovery time of mortalities and resulted in few problems. Each radio transmitter carried a label on the underside offering a reward (pencil-sketch art print) for contacting project personnel and providing information about recovered transmitters or females. We tracked radio-marked females from vehicles equipped with roof mounted four-element, null-peak antenna systems (Mech 1983). To facilitate tracking in areas frequently used by Mallards but inaccessible by trucks, we erected two 9.1-m telemetry towers near the north edge of the Mollicy Unit of Upper Ouachita NWR. Towers were accessed by all-terrain vehicles or on foot and equipped with nine-element antennas on a rotating center mast. We used fixed-wing aircraft and aerial telemetry techniques (Gilmer et al. 1981) to search for radio-marked females that could not be located from trucks and towers. We relayed these locations to ground crews who subsequently attempted to triangulate on them. Telemetry flights were conducted at 1,200-3,000 m above ground level because Cox and Afton (2000) could reliably detect similar transmitters at distances of 80 km from this altitude. To assess survival status of radio-marked females, we conducted 136 complete aerial searches of the core tracking area during the study and attempted to locate females via telemetry trucks and towers 4 times per week. We excluded the first four days of exposure (hereafter, adjustment period) for each female from all analyses to reduce potential bias due to stress from capture and handling (Cox and Afton 1998). Subsequently, we assigned daily status for each female into one of three categories for each day of the tracking period: 1) alive inside the core study area, 2) dead inside the core study area, or 3) alive or dead outside the core study area. If status was the same for consecutive tracking events, we assumed it to be constant for the days between them. When exact date of a mortality event was unknown, we estimated it as the midpoint between the last day the bird was known to be alive and the first indication of its death (Cox et al. 1998). Due to varied timing of entry into the monitored sample, emigration from the core tracking area and mortality events, the number of females included for analysis varied throughout the tracking period (Fig. 2). Mortality events were initially classified as caused by hunting, avian, mammalian or unknown sources based on hunter reports or evidence gathered at recovery sites, including damage to transmitters (e.g. bite marks), carcass condition, location of carcasses or transmitters or tracks in the vicinity (c.f. Reinecke et al. 1987; Bergan and Smith 1993; Cox et al. 1998; Fleskes et al. 2007). We classified mortality events as unknown when evidence for cause of death was inconclusive. Subsequently, we reclassified mortality events as either caused directly by hunting or other factors (combining mortalities from avian, mammalian and unknown sources). We included mortalities from unknown sources in the latter mortality estimate for consistency with previous studies (Bergan and Smith 1993; Cox et al. 1998), and because we deemed it unlikely that hunting caused the mortality of females dying after hunting seasons ended or in large areas of lands closed to hunting. We used data collected on search flights in our extended tracking area to attain emigration information. Our survival analysis excluded (right censored) birds that emigrated from the study area and those with failed radio-transmitters or that we otherwise lost contact with. When the exact date of an emigration event was unknown, we estimated it by randomly assigning the event to a day in the interval containing the true possible emigration event (Cox and Afton 2000). We included emigrating females that returned to the study area after they re-entered. Louisiana and Arkansas have split hunting seasons, with two open periods of hunting separated by a closed season. During the two years of our study, season dates were similar within the study area in Louisiana and Arkansas, with the exception that Arkansas has a one-day closure on 25 December of each year and starts its second hunting period a day earlier than does Louisiana. We divided winters ( or ) into four seasons in Arkansas and Louisiana: HUNT1 (27 Nov-5 Dec 2004 or 20 Nov-4 Dec 2005), SPLIT (6-16 Dec 2004 or 5-15 Dec 2005), HUNT2 (17 Dec Jan 2005 or Figure 2. Total number of radio-marked females included in sample for survival estimation on core tracking area by date is shown by heavy line. The light sections of the bars represent numbers of females tracked during winter and the cross-hatched sections of the bars represent numbers of females tracked during winter

4 MALLARD SURVIVAL IN WINTER Dec Jan 2006), or POST (31 Jan-10 Apr 2005 or 30 Jan-4 Apr 2006). Days were assigned to HUNT1 or HUNT2 if regular duck season was open in any portion of the core tracking area, or to SPLIT or POST when hunting seasons were closed in the entire core tracking area. Statistical Procedures Body Condition at Capture Body mass can reflect individual variation in lipid reserves as well as effects of structural size and other variables (Whyte and Bolen 1984). To account for variation in body mass associated with structural size, we first performed principal components analysis (PROC PRINCOMP; SAS Institute Inc. 2004) on five morphological measurements (natural wing chord, total tarsus, head length, culmen and middle toe; Dzubin and Cooch 1992) and then used the first principal component score as a measure of structural size for each marked female. To account for variation in body mass due to joint effects of structural size and esophageal contents, we used analysis of covariance (PROC GLM; SAS Institute Inc. 2004) to test for a relationship of body mass to structural size and esophageal content score. We treated structural size as a continuous covariate and esophageal content score as a categorical explanatory variable with three levels. Finally, we adjusted body mass of each female for her structural size and esophageal content score by adding the overall mean body mass of females to her residual from the model and used adjusted body mass as an index of body condition at time of capture (hereafter, condition; Ankney and Afton 1988; Dufour et al. 1993). Survival Choice of a survival estimator is a critical step in any survival analysis; we used the product-limit (Kaplan and Meier 1958) survival estimator in our analysis. We favor the product-limit estimator because of advantages in handling decreasing sample sizes over time and heterogeneous survival probabilities among days within seasons. Product-limit estimators require no assumptions about constancy of daily survival probabilities within seasons and can account for changing sample sizes among days due to emigration, transmitter failure or death. We used proportional hazards regression (PROC PHREG; SAS Institute) to examine variation in survival rates associated with female age, condition, winter, season and the two-way interactions between season and condition, winter and condition, and age and winter (Cox 1972; Allison 1995). We constructed candidate models containing all possible combinations of these potential covariates and used Akaike s Information Criterion values adjusted for small sample sizes (AIC c ; Akaike 1985; Burnham and Anderson 1998) to compare the relative ability of each model to explain variation in survival. We considered models with ΔAIC c 2 to be supported. Proportional hazards regression requires that the user determine a point in time where analysis will start and that time thereafter is treated as a continuous variable (Allison 1995, pp ); for our analysis, we reset the continuous time variable to the origin at the beginning of each season. We present product-limit survival estimates (Kaplan and Meier 1958) (± SE) based on factors present in our best-fit model. Hazard ratios (Allison 1995) are presented for comparisons among levels of covariates in our best-fit model; these provide ratios of effects in the context of a common time scale. Cause-specific Mortality We estimated separate survival rates for females surviving hunting and other mortality sources. When estimating survival from hunting, we right-censored data from females that died from other causes on the estimated date of death. Conversely, we censored data from females killed by hunters when estimating survival from other mortality risks. We estimated mortality rates separately for hunting and other sources of mortality by subtracting the corresponding survival rate from 1.0. Body Condition RESULTS The combination of structural size and esophogeal content score explained 35% of the overall variation in body mass among radio-marked females. Body mass was positively related to structural size (F 1, 174 = 75.8, P < 0.001) and varied significantly among esophageal content scores (F 2, 174 = 3.9, P = 0.02). Survival Our analysis included 11,912 exposure days on 174 radio-marked female Mallards. The number of females included for analyses varied throughout each winter, and declined in late winter (Fig. 2). Thirteen of 187 available radio-marked females were excluded from this analysis because they died, their transmitters failed, we lost contact with them or they emigrated from the core tracking area during the first four days of exposure. Our best-fit model included season and condition and season was present in each of the 13 top models (Table 1). The interval survival rate was highest during the relatively short SPLIT season (Table 2). Hazard ratios indicated that female Mallards were 5.6 (CI 95 = ) times and 4.4 (CI 95 = ) times more likely to die on any given day in the HUNT1 or HUNT2, respectively, than they were on any given day in the POST. The product-limit survival estimate through the entire tracking period (136 days) was 0.54 ± 0.10 (Fig. 3). The model predicted overall survival rate for the female estimated to be in the best condition was greater than twice the model predicted overall survival rate for the female estimated to be in the worst condition (Fig. 4).

5 190 WATERBIRDS Table 1. Ranking of hypothesized models, number of estimated parameters (K), differences in AICc values from the best-fit model (ΔAICc), and Akaike weights (w i ) for models with w i >.005 used to evaluate relationships of survival to female age (AGE), body condition at time of capture (CONDITION), winter of study (WINTER), season (SEASON), and two-way interactions of female age and winter (AGE*WINTER), season and condition (SEA- SON*CONDITION), and winter and condition (WINTER*CONDITION) for radio-marked female Mallards during winters and in the lower Mississippi Alluvial Valley of Louisiana and Arkansas. Model K ΔAIC c w i SEASON + CONDITION SEASON AGE + SEASON SEASON + WINTER AGE + SEASON + CONDITION SEASON + WINTER + CONDITION SEASON + CONDITION + SEASON*CONDITION AGE + SEASON + WINTER AGE + SEASON + WINTER + CONDITION SEASON + WINTER + CONDITION + WINTER*CONDITION AGE + SEASON + CONDITION + SEASON*CONDITION SEASON + WINTER + CONDITION + SEASON*CONDITION AGE + SEASON + WINTER + AGE*WINTER CONDITION Cause-specific Mortality Excluding the first four days of exposure for each female, we detected 36 mortalities on the core tracking area and attributed equal numbers of deaths to hunting and other sources. Other mortalities included those from avian (n = 9), mammalian (n = 2) and unknown (n = 7) sources. Nine deaths attributed to other causes occurred when all hunting seasons were closed. Seven deaths were originally attributed to unknown sources; three occurred during HUNT2, whereas four occurred during POST. Cause-specific mortality rates (±SE) for the entire tracking period were 0.18 ± 0.04 and 0.34 ± 0.12 for direct hunting and other sources of mortality, respectively. Figure 3. Product-limit survival estimate (solid line) on core tracking area with 95% confidence limits (dotted lines) for radio-marked female Mallards by date during winters and in the lower Mississippi Alluvial Valley of Louisiana and Arkansas. Vertical reference lines indicate the start and end of each season. Table 2. Duration of each season, survival rate (S ˆ i ), and standard error (SE) for radio-marked female Mallards by season for winters and combined in the lower Mississippi Alluvial Valley of Louisiana and Arkansas. Days were included in HUNT1 or HUNT2 if hunting seasons were open in either winter of the study for that day. Season Duration (days Interval Survival Rate HUNT SPLIT HUNT POST Ŝi SE DISCUSSION Our two highest-ranking models supported a relationship of survival to season for our radio-marked sample. In particular, females were more likely to die during days when hunting seasons were open than during days when hunting seasons were closed. We suspect that females are likely to move more as a response to increased disturbance during the hunting season and therefore may be exposed to increased mortality risks from all sources.

6 MALLARD SURVIVAL IN WINTER 191 Figure 4. Model predicted survival through the entire tracking period (136 days) by female body condition at time of capture (solid line) and 95% confidence limits (dashed lines) for radio-marked female Mallards during winters and in the lower Mississippi Alluvial Valley of Louisiana and Arkansas. Our best-fit model contains only one more parameter and has an AIC c score of 0.38 lower than our second best model; we interpreted this as modest support for a direct relationship of female survival to body condition. Bergan and Smith (1993) reported a similar effect of condition on survival of Mallards in Texas. We measured body condition once for each female, four days prior to her entry into the dataset. Thus, the relationship of survival to body condition may indicate that females in poor body condition during early winter remain more susceptible to mortality throughout the entire wintering period. Hunter-killed Mallards have previously been found to be lighter than Mallards initially marked in the LMAV (Hepp et al. 1986; Heitmeyer et al. 1993); however, no relationship between condition and survival from hunting was found in our marked sample (Davis 2007). Thus, we suspect that condition had a greater effect on mortality from other sources than on mortality from hunting in our study. Our top two models showed no support for relationships of survival with female age or winter of study. Our failure to find strong relationships between female age and survival may have been due to the relatively late capture of females in our study. Immature females that survived until arrival in our study area may have gained experience that enabled them to survive as well as adults during winter. Weather and water conditions may influence survival rates in wintering populations of waterfowl. Weather varied markedly between the two winters of our study; cumulative precipitation from 1 August 2004 through 1 January 2005 was about 15 cm > the 30-year average for that time period, whereas cumulative precipitation from 1 August 2005 through 1 January 2006 was about 25 cm < the 30-year average near Bastrop, LA (Davis 2007). We suspect that the failure to find effects of winter on survival of female Mallards in our core tracking area, despite considerable differences in water levels, was due to variation in emigration rates between the two years of the study. For the majority of the tracking period, fewer females remained on our core tracking area in than in (Fig. 2). Females may have emigrated to other areas with better water conditions in Overall, the lack of a strong relationship between winter and survival suggests that Mallard survival rates in the LMAV do not vary with habitat conditions; however, the opposite was documented for Northern Pintails (Anas acuta) in other wintering areas (Moon and Haukos 2006). With the exception of one cohort of mallards wintering in California, our survival estimate for radio-marked female Mallards was less than those reported for similarly marked mallards in the LMAV, Texas and California (Reinecke et al. 1987; Bergan and Smith 1993; Fleskes et al. 2007). Differences exist in analytical methods between our study and previous work in the LMAV, but comparison of survival rates using the methods outlined by Heisey and Fuller (1985) confirmed that female survival during our study was less than survival reported in earlier estimates (Davis 2007). Overall, recent estimates of non-breeding season Mallard survival derived from Mallards marked with Dwyer (1972) type backpack transmitters were lower than estimates reported in previous studies of similarly marked females. Comparison of previous studies demonstrated heterogeneity in survival rates among seasons in the

7 192 WATERBIRDS LMAV (see Reinecke et al. 1987; Dugger et al. 1994). Female Mallards in our study of the LMAV and those in the Playa Lakes region of Texas had lower hunting mortality than mortality from other sources, but the reverse was found in earlier studies in the LMAV and in California (Reinecke et al. 1987; Bergan and Smith 1993; Fleskes et al. 2007). A previous study reported no deaths occurred in late winter for 92 female Mallards marked after hunting seasons in the LMAV (Dugger et al. 1994), whereas we documented seven deaths (19% of our total detected mortalities) after hunting seasons closed in our study area. Thus, our results indicated that other mortality may be more prevalent now than during earlier studies in the LMAV. Moreover, the overall reduction in survival reported in our study compared to previous studies in the LMAV appeared to reflect increased other mortality. Due to consumption of some carcasses by predators and scavengers, hunting could not be completely ruled out as a contributing factor to deaths classified as other mortality in our study. Further, all mortalities originally classified as unknown were categorized as other mortalities for analyses, which may have inflated our other mortality estimate. However, four of seven mortalities originally classified as unknown occurred 10 days after hunting seasons closed, so we considered it less likely that these deaths were related to hunting than to other sources of mortality. Based on timing of mortalities and juxtaposition of recovered carcasses, we deemed misclassification of mortality to be minimal in our study. Categorization in this manner is analogous to methods used for other studies, wherein birds lost due to crippling are indistinguishable from birds succumbing to nonhunting related sources of mortality. Our estimates may have been subject to potential biases that caused overestimation or underestimation of survival. Daily survival estimates were derived from smaller samples of females as winter progressed; thus, mortalities near the end of our tracking season had a larger impact on survival estimates than did mortalities near the beginning of our tracking period and introduced decreased precision. In one banding study, male Mallards banded on areas closed to waterfowl hunting seemingly survived at higher rates than those banded on areas open to hunting (Blohm et al. 1987). Our entire sample was marked on areas closed to hunting, so survival probabilities may have been overestimated. However, females in our study used areas closed to hunting only 21-42% of the time during diurnal sampling periods (Davis et al. 2009). Radio-marking may negatively impact behavior and survival of waterfowl (Withey et al. 2001), but Fleskes (2003) suggests that backpack transmitters may be appropriate for use during the nonbreeding season. Other studies have documented very high winter survival rates on other species of dabbling ducks using this type of transmitter. For example, Migoya and Baldesarre (1995) reported winter survival rates averaging on Northern Pintails, and Moon and Haukos (2006) reported a winter survival rate of during one winter of their study; these high rates of survival suggested that bias in telemetry-based studies on wintering ducks may be minimal. Further, we acknowledge that selective harvest for marked individuals may have occurred, but believe that these effects were minimal in our study; all hunters reporting harvest of radiomarked females indicated that they were unaware that shot females were marked until after they retrieved them. If increasing female Mallard survival becomes a conservation objective for the LMAV, several strategies might be implemented. Female Mallards in forested wetlands were less likely to switch habitats and moved shorter distances than did females in other habitats (Davis and Afton 2010); reduced movements could result in increased survival by reducing exposure to risks. Conservation programs which encourage restoration and maintenance of forested wetland habitats may be important to Mallards wintering in the LMAV. Also, restoration of habitats, especially forested wetlands promoting dense understories that provide protection from avian predators in this area, may improve winter survival of female Mallards.

8 MALLARD SURVIVAL IN WINTER 193 Practices that directly reduce predator abundance or that may deter predators on wintering areas containing large concentrations of Mallards also may decrease mortality. Hunting mortality potentially could be decreased by manipulating habitats or closed zone boundaries to include more forested wetland habitats that are frequently used by female Mallards in this area (Davis et al. 2009). Louisiana and Arkansas both implement split regular duck hunting seasons utilizing two periods of open hunting. Female Mallards may have been more susceptible to mortality from harvest near the beginning of hunting seasons (Davis 2007); thus, a continuous season, without splits may result in lower hunting mortality. Based on estimated winter survival rates of 0.80, sensitivity analyses have demonstrated little effect of variation in winter survival on population growth rates of Mallards (Hoekman et al. 2002). These models could be reevaluated in light of lower survival rates reported in this study and other recent studies. Despite variable water conditions in our study area, survival rates during the two years of our study varied little; additional study of Mallard survival in winter could provide valuable information about geographic and temporal variability in survival rates. Further, studies which directly measure effects of management practices on condition and female Mallard survival would benefit managers in the LMAV. Estimates of seasonal survival of other waterfowl wintering in the LMAV are limited; studies evaluating survival of other species in this area would benefit conservation planners. ACKNOWLEDGMENTS Financial and logistical support were provided by Louisiana Department of Wildlife and Fisheries, Ducks Unlimited, Inc., USFWS, USGS-Northern Prairie Wildlife Research Center, and the School of Renewable Natural Resources, Agricultural Center, Graduate School and USGS-Louisiana Cooperative Fish and Wildlife Research Unit at Louisiana State University. We thank C. Booth, M. Chouinard, S. Durham, D. Ellerman, G. Gooding, A. Hammond, J. Hanks, R. Helm, J. Johnson, L. Lewis, K. McCarter, T. Moorman, K. Ouchley and B. Strader for support. C. Coates, J. Ferguson, P. Finley, M. Lyons, C. Odom, T. Michot and A. Nygren piloted planes during aerial surveys. J. Rataczak provided artwork used as a reward to hunters for information on recovered radio-marked females. T. Arnold provided advice on model fitting. J. Moon, T. Moorman, F. Rohwer and several anonymous reviewers provided comments on the manuscript. We thank our crew of technicians, J. Bolenbaugh, J. Denton, J. Rainbolt, A. 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